(1) Field of the Invention
The present invention relates to a power-supply control system for peripheral equipment of a computer. More particularly, it relates to a power-supply control system which automatically cuts off the alternating current (AC) input power to the peripheral equipment when a user who has worked on a computer stops working on the computer for a predetermined period of time. It again supplies the AC input power to the peripheral equipment when the user resumes his work on the computer.
(2) Description of the Prior Art
Due to the wide spread use of personal computers, the demand for peripheral equipment, such as monitors and printers, has increased. In fact, many view this equipment as indispensable and essential for the proper use of personal computers.
In conventional systems, power is continuously applied to the peripheral equipment even after a user stops working on the computer. Thus, if a user does not intend to use his peripheral equipment for a period of time, he must remember to turn off the power switches to that peripheral equipment, otherwise electrical power is wasted through the continuous AC input power supplied to this equipment.
In order to solve this problem, the Korean Utility Model Publication No. 91-3424 (filed on Dec. 31, 1987) entitled "Power-Supply Control Circuit of Television" discloses a technique for preventing this waste of power. This technique involves automatically turning off the power of a monitor, when no video signals are detected at its input. Such a technique is also disclosed in both Korean Utility Model Publication No. 91-3423 (filed on Dec. 31, 1987) which is entitled "Power-Automatically Turn-Off Circuit of Monitor", and Korean Utility Model Publication No. 90-8961 (filed on Nov. 29, 1985) which is entitled "Power-Automatically Cut-Off Circuit of Monitor".
In the above-mentioned "Power-Supply Control Circuit of Television" publication, control of a switching transistor in a switched mode power supply (SMPS) may be attained through the existence of video signals which are supplied to a video input stage of the monitor. Thus, the power of a television is automatically turned on or turned off corresponding to the existence of this signal. Similarly, the monitor of the "Power-Automatically Turn-Off Circuit of Monitor" publications automatically turned off when no video signal is present from the connected computer. Also, the "Power-Automatically Cut-Off Circuit of Monitor" disclosure automatically cuts off the power supplied to the monitor when the no keyboard input exists for a predetermined period of time during system use, where power to the monitor is resumed when input to the keyboard detected.
However, contrary to a television, a computer monitor has a continuously input video signal which exists regardless of its data flow. Since the conventional power-supply control circuit of a television cuts off power to its monitor on the basis of the existence of a video input signal, this circuit is not effective for computers or computer monitors which always have an input signal. In addition, this circuit may not be applied to a monitor which does not use a SMPS.
Similarly, the "Power-Automatically Turn-Off Circuit of Monitor" publication described above is not effective for computer monitors because it is based on the existence of the monitor input signal. Further, this circuit can only be applied to a device in which transmitting data is performed in series, such as a monitor. It cannot be applied to a device in which transmitting data is performed in parallel, such as a printer.
Finally, the "Power-Automatically Cut-Off Circuit of Monitor" publication concerns a circuit for sensing when data has not been input from the keyboard for a predetermined period of time. Because this circuit relies wholly on the input from one device, namely the keyboard, it neglects all other input and output devices such as a mouse, a series communication port or a parallel communication port. Thus, in the middle of an input/output operation through means of another input/output device, this system cuts off power to the monitor which may result in operator error.